Technical Field
The present invention relates to a defect review techniques for observing defects on samples detected by inspection devices to acquire detailed information of the observed defects.
Background Art
In manufacturing processes for such as semiconductor devices, processes such as film formation, lithographic exposure, or etching are repeated to form micro-circuit patterns on semiconductor samples via hundreds of processes (hereinafter, semiconductor samples are referred to as samples). In these manufacturing processes, decrease in yield rate may be caused by foreign particles generated on the sample due to errors or improper maintenances of process manufacturing devices or to mismatch in manufacturing conditions, or may be caused by abnormal appearances such as disconnection or short-circuiting of circuit patterns formed on the sample. Thus it is necessary to promptly identify the cause of foreign particles generated on the sample or of abnormal appearances of circuit patterns, and to take measures for them immediately. Hereinafter, foreign particles or abnormal appearances of circuit patterns will be referred to as defects.
As countermeasures for defects generated on samples in manufacturing processes of semiconductor devices, a method for estimating the cause of defects is known in which: the defect on the sample is detected by an inspection apparatus to acquire positional information of the defect; the defect on the sample is observed in details using electron microscopes (Scanning Electron Microscope, hereinafter referred to as SEM) according to the positional information; and if necessary, automatic classification of the defect is performed using ADC (Automatic Defect Classification) or elemental analysis is performed using EDS (Energy Dispersive X-ray Spectroscopy).
As inspection apparatuses, SEM-type inspection apparatuses and optical inspection apparatuses are known. SEM-type inspection apparatus: irradiates a primary electron beam onto the sample; acquires, by detecting a secondary electron generated from the sample, a SEM image of the defect portion; and acquires positional information of the defect according to a difference between the acquired SEM image and a SEM image of a reference portion. Optical inspection apparatus: irradiates light such as laser onto the sample; and detects reflected light or scattered light generated from the sample, thereby acquiring positional information of the sample.
Defect review apparatus, according to the positional information of the defect on the sample received from the inspection apparatus, rapidly acquires detailed information of the defect portion by a functionality referred to as ADR (Automatic Defect Review) that automatically captures SEM images of the defect portion.
Due to the difference of stage mechanical systems or of signal detection schemes between inspection apparatuses and defect review apparatuses, the defect coordinate systems generated in both apparatuses include misalignments from each other. Therefore, when the defect review apparatus attempts to acquire SEM images of the detect portion using the coordinate information of the defect received from the inspection apparatus only, the defect may be departed from the field of view of SEM. Thus a rough matching of coordinate system, referred to as global alignment, is typically performed between the inspection apparatus and the defect review apparatus before performing ADR. The global alignment is performed using alignment patterns or sample surface edges (edge portions). However, it is hardly likely that the defect is captured within the field of view of SEM only by global alignments.
In order to address the above-described problem, a method referred to as file alignment is used. Fine alignment is a method in which: coordinate information of representative defects on the sample is acquired before observing the sample using SEM; and the defect coordinate system defined by the inspection apparatus is converted into the defect coordinate system defined by the defect review apparatus. As a result of fine alignment, most of defects on the sample will be likely to be captured within the field of view of SEM. Fine alignment is particularly important as a method for correcting coordinates when observing defects on non-patterned samples, on which there is no specific patterns used for reference position alignment of defect coordinates and thus the defect coordinate acquired from the inspection apparatus is inaccurate.
Patent Document 1 listed below describes, regarding coordinate misalignments between inspection apparatus and defect review apparatus, that the defect is observed using a plurality of optical conditions (0013). It further describes as specific methods that an optical filter 514 and illumination intensities are adjusted (0077).
Patent Document 2 listed below describes a method for expanding the field of view to search defects in cases where the defect is not within the field of view even after performing fine alignment.
Patent Document 3 listed below describes about Dark Field Optical Microscope (DFOM). Fine alignment for non-patterned samples is typically performed using optical microscopes which field of view is wider than that of SEM. Specifically, DFOM is typically used which is capable of detecting micro defects by detecting scattered light. Patent Document 3 attempts, by adding light adjusting functionality such as dimming filter, deflecting filter, or wavelength filter, to correctly reflect the defect shapes onto DFOM images so that the reliability of coordinate correction is improved.
Regarding non-patterned samples which defect coordinates acquired from inspection apparatus is inaccurate, it is hardly likely that all defects for observation are captured within the field of view of SEM only by performing fine alignment to representative defects on the sample. Thus it is preferable to perform fine alignment to all defects for observation. Since there are tens to thousands of defects for fine alignment per sample, fine alignment is typically performed by automated sequences referred to as automatic fine alignment.